The present invention is directed to a protection circuit and, more particularly, to an on-chip surge protection circuit.
Current and voltage spikes (i.e., energy spikes) can damage electronic circuits. Energy spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit. Such spikes can be caused by, for example, electro-static discharge (ESD) events. An uninterrupted voltage increase that typically lasts for about 50 uSec is called a “voltage surge” rather than a spike. Since voltage spikes and surges can damage sensitive electronics, many circuits include ESD and surge protection circuitry.
FIG. 1 is a schematic circuit diagram of a conventional ESD protection circuit 10, which includes an AC trigger circuit 12 and an ESD protection device 14. The AC trigger circuit 12 includes first and second resistors R1 and R2, a capacitor C1, and a P-type transistor MP1, while the ESD protection device 14 comprises a large N-type transistor MN1. When an ESD pulse occurs, the current charges the capacitor C1, which turns on the transistor MP1. The transistor MP1 and the resistor R2 in turn bias the transistor MN1, and then the transistor MN1 conducts the ESD generated current to ground.
However, the ESD protection device 14 is only active for a very short time (several hundreds of nanoseconds or less), which may be much less than the period of a surge event, which typically has a pulse duration of around 50 μs or longer. Thus, the conventional ESD protection circuit 10 does not adequately handle surge events.
Accordingly, it would be beneficial to have an ESD protection circuit that also can protect against surge events.